1. Field of the Invention
This invention deals with the arrangements and methods for controlling electronic communications switching equipment such as Asynchronous Mode Transfer (ATM) or frame relay switches.
2. Description of the Prior Art
ATM switching is used in communications systems for switching voice, data, and video information. Frequently these services are supported simultaneously by the same switch. This technology is applied in areas including local and wide area networks, two way cable to the home networks, Internet access, and corporate enterprise networks. The cost and efficiency of the switch are key components in the overall cost of the system. Hence, an improvement in switch capacity would provide benefits in many applications.
Many modern electronic communications switches are capable of switching small elements of information, called cells, rapidly between an input port and an output port. A header at the beginning of each cell contains identifying information that may also be modified in the course of this switching. The switches typically accomplish this using connection control tables, stored in a specialized memory in the switch. One important measurement of the capacity of the switch is the number of connections that can be accommodated, i.e. the number of entries in the control tables and in the corresponding underlying switch hardware that uses the control tables.
In prior art, each connection supported by the switch occupies at least one entry in one or more of the connection control tables. Reducing the number of connection entries required in the switch would reduce the cost and complexity of the switch hardware. The present invention reduces the number of connection entries required in the switch, thus reducing the cost and complexity of the switch hardware.
In existing communications switches, at any one time, not all of the connections represented by the entries in the connection control tables are actively in use. This most frequently occurs when the cells contain data representative of computer data, rather than voice or video data. Such data typically comes in bursts interspersed with pauses that can be relatively long. During the pauses it is possible to temporarily remove the connection from the switch during these periods of inactivity thus freeing up the switch capacity for other connections.
Accomplishing this requires rapid control of the switch connection tables. The process of controlling these tables is referred to herein as connection caching. It is reminiscent of memory caching commonly used in the microprocessor industry.
Previous switches use control tables as disclosed in U.S. Pat. No. 5,479,401 by Bitz et al. Bitz et al. provides a table lookup mechanism using information found in the ATM cell header. However the entries in these tables are defined over the life of a connection. Bitz et al. does not modify these tables dynamically, based on current activity.
U.S. Pat. No. 5,067,123 by Hyodo, et. al. discloses a table circuit registering virtual channels presently formed in the ATM switching network in a management table, and a receiving part for receiving communication request from one of the terminals and for determining whether or not the management table registers a virtual channel corresponding to the communication request. It also contains a virtual channel setting part that registers the virtual channel in the management table. This is essentially a table look up mechanism with the added feature that an entry can be added dynamically when needed. However, Hyodo et al. deals with the control table that provides the actual switching information, and does not use a table lookup for a connection cache function, that is to determine if the management table within the switch presently has an entry corresponding to the incoming communication request.
U.S. Pat. No. 5,521,923 by Willmann et al. provides a method of temporarily storing data packets in two or more queues on the basis of data contained in the incoming packets. All of the queues share a common buffer memory, and cells not accommodated by the queues and memory are rejected. This is essentially a congestion control method to enable the switch to accommodate momentary overload conditions. However, Willmann et al. does not disclose a means for detecting idle connections due to aging and does not perform connection caching.
Pfeiffer et al. in U.S. Pat. No. 5,535,366 discloses a method of reclaiming unused resources in an ATM switch wherein the communications resource (e.g. the memory locations of the buffer) have an associated label marking the resource as being free or used, and have an associated time of entry stamp. All memory locations are checked at regular intervals for the age of their contents. Upon attainment of a predetermined age, the location is labeled as free. In Pfeiffer et al. the memory is normally marked free after use, however, error conditions can fail to mark the memory free, thus leaving it blocked for subsequent use. An object of the Pfeiffer invention is to discover these error conditions and correct them. Pfeiffer et al. does not use an aging algorithm to discover idle connections.